Influence of Sulfate on Fe-Oxide Formation: Comparisons with a Stream Receiving Acid Mine Drainage1

K. S. Brady2, J. M. Bigham, W. F. Jaynes and T. J. Logan
Department of Agronomy, The Ohio State University, Columbus, Ohio 43210
1 Journal article No. 131-85.
2 Present address: Tennessee Valley Authority, T-218 NFDC, Muscle Shoals, Alabama 35660.

Abstract: An ochreous precipitate isolated from a stream receiving acid-sulfate mine drainage was found to consist primarily of goethite and lesser amounts of ferrihydrite-like materials. The Fe-oxide fraction, including goethite, was almost totally soluble in acid ammonium oxalate. Similar materials were produced in the laboratory by hydrolysis of ferric nitrate solutions containing 250 to 2000 µg/ml sulfate as Na2SO4. Initial precipitates of natrojarosite transformed to Fe-oxides upon aging for 30 days at pH 6.0. The proportion of goethite in the final products decreased with increasing sulfate (SO4/Fe = 0.2 to 1.8) in the initial hydrolysis solutions; only ferrihydrite-like materials were produced at SO4/Fe ratios > 1.5. Variations in SO4/Fe solution ratios also produced systematic changes in the color (10R to 7.5YR) and surface areas (49 to 310 m2/g) of the dried precipitates, even though total S contents were relatively constant at 2.5 to 4.0%.

Key words: Acid mine drainage • Feroxyhite • Ferrihydrite • Goethite • Iron • Natrojarosite • Sulfate

Clays and Clay Minerals; June 1986 v. 34; no. 3; p. 266-274; DOI: 10.1346/CCMN.1986.0340306
© 1986, The Clay Minerals Society
Clay Minerals Society (www.clays.org)